A multidisciplinary study of invisible gold in arsenopyrite from four mesothermal cold deposits in Siberia, Russian federation

Characterization of gold in four Siberian mesothermal gold deposits was done through a multidisciplinary investigation (including ore microscopy, INAA, SIMS, EPMA, and Au-197 Mossbauer spectroscopy). The deposits are Olympiada and Veduga in the Enisei Mountain Range and Nezhdaninskoye and Sentachan in the Verkhovansk-Kolyma area, in which vein and disseminated orebodies are hosted by sedimentary sequences metamorphosed to amphibolite (Olympiada) and greenschist facies. Ore minerals include arsenopyrite and pyrrhotite (or pyrite) as major constituents with minor scheelite, and sphalerite, chalcopyrite and native gold as minor constituents (with +/- aurostibite, galena, gudmundite, tetrahedrite, stibnite, and berthierite). Some of the gold mineralization is metallurgically refractory in all four deposits, largely due to the presence of "invisible" gold in arsenopyrite, and to a lesser extent, in pyrite. Several generations of arsenopyrite are recognized in the auriferous zones of the Veduga, Nezhdaninskoye, and Sentachan deposits. Textural observations indicate late deposition of native gold with respect to arsenopyrite. No evidence was found of arsenopyrite recrystallization and the crystallization of native gold is considered to result from an evolution of fluids rather than redeposition of gold. Wide variations in the gold contents of arsenopyrite occur within deposits, within samples, and within individual grains. INNA. analyses of individual arsenopyrite grains (30-70 mu m in size) show that the gold concentration ranges from